Data access formatter

ABSTRACT

The defined architecture allows for format-efficient data storage on bit-patterned media, while allowing for typical variations in the drive, such as reader to writer gap variations. The defined BPM architecture relaxes some timing requirements on real-time signaling from the formatter to the channel, while enabling bit-accurate alignment between data accesses and the media.

SUMMARY

The detailed description describes a data format. A formatter providesdata access information and a signal to indicate the data accessinformation is ready for transfer. The signal, however, may not be usedto initiate a data access. For example, a channel may use the signal tolatch the data access information, but may use its own internallygenerated signal, which can be independently derived instead of usingthe signal, to initiate the data access. Also disclosed is a dataformatting method comprising outputting a fragment descriptor for a dataaccess and outputting a signal that indicates the fragment descriptor isavailable and that is timed independent of a start of the data access.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 a illustrates a device that uses bit-patterned media;

FIG. 1 b is a block diagram of components shown in FIG. 1 a;

FIGS. 2 a and 2 b illustrate a data format for a data wedge;

FIG. 3 illustrates two data wedges split by a servo wedge;

FIG. 4 illustrates an intersector gap between two data sectors;

FIGS. 5-7 illustrate intersector gap interleaving with Q and/or Pfields;

FIG. 8 is a flowchart of a calculation for an intersector gap;

FIG. 9 illustrates data regions without certain overhead;

FIGS. 10 a and b show a data wedge and corresponding fragmentdescriptors; and

FIG. 11 is a timing diagram of an interface shown in FIG. 1 b.

FIG. 12 discloses a formatter and a channel coupled to one of a tape,optical, and data stream.

FIG. 13 illustrates a method for the use of RS and WRS.

DETAILED DESCRIPTION

The capacity of a storage device, such as a disc drive, can be increasedby using bit-patterned media (BPM). Such a disc drive is shown in FIG. 1a. Disc drive 10 includes BPM 20 that stores data on tracks, one shownas track 25. In some embodiments BPM 20 may also be a heat assistedmagnetic recording medium that includes features to enable thattechnology. Data on track 25 is accessed by a transducing head 35 on anactuator arm 30, a preamplifier 40, a channel 50 and a formatter 60.

BPM 20 is constructed with isolated areas (referred to as “dots” or“islands”) of the magnetic material of BPM 20, each dot intended tocontain one bit of data or more than one bit of data in a multilevelembodiment. To illustrate, track portion 25′ is shown that includes datawedges 27 and servo sectors 29. Data wedges 27 include dots 28 that areused for storing data and overhead information. Each dot is separatedfrom its adjacent dots by regions of non-magnetic material. There can bethousands, millions or more of dots for each data wedge.

Servo fields 29 are used by components of disc drive 10 to obtainposition information such as the number of the track that transducinghead 35 is tracking, the circumferential position of transducing head 35relative to that track, fine positioning information that is used tokeep transducing head 35 on that track, etc.

To write data to BPM 20, formatter 60 receives data on bus 65. The datacan be from a system or host using disc drive 10, or can originate fromwithin disc drive 10. Formatter 60 formats the data for each data wedge27, then sends the formatted data to channel 50. Channel 50 encodes theformatted data for storage on BPM 20. In the meantime, channel 50 isalso synchronized with the dots on a BPM track so that channel 50 cantimely provide the encoded, formatted data to preamplifier 40.Preamplifier 40 transmits the signal representing the encoded, formatteddata to transducing head 35. A writer (not shown) of transducing head 35then interacts with a BPM track to write the encoded, formatted data.Reading of data from a BPM track is processed in reverse of the mannerdescribed.

FIG. 1 b shows the interaction of preamplifier 40, channel 50 andformatter 60 in more detail. The interface protocol between channel 50and formatter 60 contributes to the use of the disc drive of the BPM andthe data format explained immediately below. The general interfacebetween channel 50 and formatter 60 includes a clock interface thatincludes NRZ_CLK and WRT_CLK, and a control interface that includes RS,WRS, STARTING_WS, ENDING_WS, FRAG_START, FRAG_LEN, FRAG_NUM, END_OF_SCTRand BLOCK_INFO. The general interface also includes a data interfacethat includes NRZ_RDATA, NRZ_EP, RDATA_VALID, NRZ_WDATA, NRZ_PARITY,WDATA_VALID, CBF, CHAN_RDY, and FLAW_SCAN_BUS. More details of thisgeneral interface will be provided later in this description. Data ispassed between preamplifier 40 and channel 50 on READ_DATA andWRITE-DATA bus.

BPM 20 also contains embedded timing burst patterns (not shown) that areformatted into the dots 28 of data wedges 27 at preferred regular timingintervals. These embedded timing burst patterns are referred to as iPLL(interspersed phase-locked loop) fields or “P fields.” The P fields canhave a different physical dot pattern than the dots for the remainingpart of the data wedge. Circuitry in the disc drive, particularlychannel 50, uses the P fields to obtain phase and frequency clocksynchronization with the dots 28 on BPM 20. The timing interval betweenthe P fields is based on a magnitude and a bandwidth of tolerable timingdisturbances between channel 50 and BPM 20. Specifically, the frequencytolerance and interval between P fields is chosen to ensure that undersustained operating conditions an accumulated phase error stays limitsfor reliable writing.

FIG. 2 a shows a single BPM data wedge between two servo fieldscontaining multiple P fields. P fields 210, 214, 216 break data wedge220 between servo fields 30, 32 into multiple data regions 240, 242,243, 244, 245, 246, 248. During write operations the P fields 210, 214,216 are read to obtain timing phase information to feed back into thedata phase-locked loop (PLL) of the channel. While the reader (notshown) of the transducing head is reading the P fields 210, 214, 216,the writer is “quiet.” The writer is either not energized or writing aDC field to avoid inducing noise into the reader or read signal. Tofacilitate this, quiet fields 50, or “Q fields,” are formatted onto themedia prior to each P field 214, 216 since the writer trails the readerin the transducing head. The precise location of each Q field 50relative to its associated P field can vary from head to head and fromtrack to track due to the variations in the effective reader-writer gap.Since no data is written in the date wedge 220 prior to P field 210, noassociated Q field is used. Additionally, the data sector fragments 243,245 between the Q and P fields are referred to as a “runt data sectorfragments.”

The placement and length of each Q field can be determined duringmanufacturing and saved for each track and potentially each zone. Duringthat time all the transducing heads of a disc drive are characterized,particularly the reader-writer gap for each transducing head and eachzone of each surface of each BPM in the disc drive. A zone can consistof multiple tracks that have characteristics similar enough that theycan all be treated the same for purposes of accessing data stored onthem. For example, a zone can have multiple tracks that have the sameformat and the same data frequency.

FIG. 2 b illustrates a zone that includes radially-aligned data wedgesof tracks 0-N. Servo sectors 201 bound Q and P fields 202, 203, datasector fragments 204, and gaps 205 before and after the servo sectors.As shown, Q and P fields are radially aligned. The Q and P fields can beindividually and collectively considered as “transducing head overhead.”

Tracks 0-N constitute a zone of the BPM. As such, tracks 0-N havesimilar characteristics so that the disc drive firmware can easilycontrol access to them. For example, the data wedges have the samenumber of dots between servo sectors 201.

Turning back to FIG. 2 a, illustrated is a larger scale data wedgeportion 220′ of the data wedge 220 showing the relative positions for Qfield 250 and P field 216. Data wedge portion 220′ is composed ofseveral defined areas on the media called “symbols” that are shown assquares in data wedge portion 220′. Each symbol is 12 bits (dots) long,for example.

P fields are preferably aligned to symbol boundaries, and can includepad bits in the beginning and/or end symbols to facilitate the symbolalignment. P fields can also include a synchronization pattern.Preferably Q field 250 is sized at least one symbol larger than itsassociated P field 216 since the reader-writer gap may not be an integernumber of symbols. To illustrate, the reader-writer gap is shown toextend from the first symbol of P field 216, back to symbol 270immediately after postamble 260. Since P field 216 is 4 symbols long, Qfield 250 includes symbol 270 and the immediately following foursymbols. Also, the effective reader-writer gap varies with thetransducing head skew angle, so the position of the Q field relative tothe P field is dependent on the radial position of the data track withinthe zone. The size of the Q fields is preferred constant across suchzone, or at least on the same track.

The disc drive firmware determines the size of the runt data sectorfragment 245 between Q field 250 and P field 216, based on thereader-writer gap of the corresponding transducing head at thecorresponding data track. In FIG. 2 a the number of symbols between thebeginnings of the Q and P fields is 12, so 12 minus the 5 symbols of Qfield 250 leaves 7 symbols for runt data sector fragment 245, includingpreamble 265 and postamble 260.

Preamble and postamble fields 265, 260 shown in FIG. 2 a preferably areused immediately before and after every area of contiguous data tosupport the decoder function in the channel that recovers the actualbits from the encoded bits on the BPM. These fields preferably are onesymbol each. The preamble and postamble fields do not have to be thesame size, but each are the same size for the entire track andpotentially a zone.

Due to the unipolar nature of the P field media pattern (e.g., ++00) thesignal read from the P field may not be sufficient to serve as validpreamble or postamble data for the decoder of the channel. Therefore, apostamble field is used before every P field, and a preamble field isused after every P field for the decoder. Since the Q field is writtenas a DC pattern over data-patterned media, it has different read-backcharacteristics than the P field, and the Q field may not have to use apostamble field or a preamble field. However, as shown in FIG. 2 a, thepreamble and postamble fields 265, 260 are used around both P and Qfields, and they are each one symbol long. Each preamble and postamble,if used, associated with respective Q and P fields is also part of thetransducing head overhead.

During read operations the channel skips the Q fields 50 and reads the Pfields 210, 214, 216 of data wedge 220 to maintain the channel PLLsynchronization with the BPM. Even if some of the sectors are beingskipped (for example, they are not part of the requested blocktransfer), the channel still reads and demodulates the P fields. Notethat a gap before servo 262 compensates for the reader-writer gap andwrite-to-read recovery time when switching from writing data to readingservo data. A gap after servo 264 may be used to support servo-recoveryto data-recovery switching time and for recording special data fields,such as repeating run-out and repeating timing run-out fields, ifneeded.

Referring to FIG. 3, a data sector is shown that is split on a track bya servo sector. Servo sector 310 is interposed to a data sector fragment320 and a data sector fragment 330 of data sector N. In the case whereservo sector 310 contains bipolar (e.g., ++−−) data fields such as arepeatable run-out compensation field, the preamplifier should be turnedoff while the transducing head is over servo sector 310. In that case,write splice (WS) 340 is placed at the end of the data sector fragment320 to accommodate the time the preamplifier takes to turn off its writecurrent. Write splice (WS) 350 also is placed at the beginning of thedata sector fragment 330 to accommodate the time the preamplifier takesto turn on the write current. The size or length (or duration) of awrite splice represents a current transient in the writer circuit thatwould interfere with any read operation, such as recovering a P field.In addition, preamplifiers can produce a high-frequency “degaussing”burst to the writer shortly after switching out of write mode. Thatdegaussing is also taken into account in determining the WS duration. Ifservo sector 310 does not have bipolar data fields, the preamplifier canbe left on while the transducing head is over servo sector 310. Withthis configuration WS 340, 350 can be eliminated, and a more efficienttrack format is had.

In addition, preferably a preamble field is placed at the beginning ofevery data sector fragment after a write splice (as shown in FIG. 3, forexample) if the write splice exists at the beginning of the fragment.Similarly, a postamble field is placed at the end of every data sectorfragment before a write splice if the write splice exists at the end ofthe fragment. Regardless of where they are used in the data wedge, eachpreamble is the same symbol length and each postamble is the same symbollength. The same is true for the entire track and potentially the zone.

To support random access of the data on the BPM, in which any singlesector on the media can be read or written individually, the data formatincludes intersector gaps (ISGs) between sequential data sectors.Referring to FIG. 4, an ISG 410 includes a postamble field 420immediately at the end of data sector fragment 430, a write splice (WS)field 440 shared by both data sector fragments 430, 450 for optimumformat efficiency, and a preamble field 460 immediately preceding datasector fragment 450. ISG 410 also includes a predetermined number ofextra symbols 470 to accommodate P and Q field interruptions of the ISG410, in which cases the position of the WS 440 may have to move laterthan its preferred earlier position. As an example, ISG 410 can bethirteen symbols wide with postamble 420 and preamble 460 being onesymbol each, WS 440 being seven symbols, and extra symbols 470 beingfour symbols. FIG. 4 represents an ISG that occurs in a portion of adata wedge away from any Q or P field.

If only data sector fragment 430 is written, the channel turns off thepreamplifier write current at the beginning of WS 440. If only datasector fragment 450 is written, the channel turns on the preamplifierwrite current at the beginning of WS 440. If both data sector fragmentsare written back-to-back, the write current remains on during the entireISG.

When the data wedge format produces an ISG that is interrupted by a Q orP field, the formatter determines the correct location of the writesplice. In FIG. 5, the ISG is thirteen symbols long and includespostamble 510 (one symbol), WS 520 (seven symbols) that includes symbol560 (explained below), extra symbols 530 (four symbols) and preamble 540(one symbol). The ISG is interrupted by Q field 550. The number ofsymbols 580 between the end of data sector fragment 570 and thebeginning of Q field 550 is eight. The formatter determines that thereis enough symbol area between the end of data sector fragment 570 and Qfield 550 for WS 520 to be placed before Q field 550 along withpostamble 510. Note here that WS 520 is allowed to use the symbol area560 reserved for the postamble immediately before the Q field becausethe ISG already includes postamble 510 for data sector fragment 570.Thus there is no need to use symbol area 560 for a postamble immediatelybefore Q field 550.

Extra symbols 530 and preamble 540 start immediately after Q field 550in the runt data sector fragment between Q and P fields 550, 595. Extrasymbols 530 start in the symbol immediately after the Q field that isreserved for the preamble. Since the ISG already includes preamble 540for data sector fragment 590, the reserved preamble symbol does not haveto be used as such.

In FIG. 6, an ISG (including postamble 610, extras symbols 620, WS 630and preamble 640) occurs in the track layout one symbol later than inFIG. 5, and is interrupted by Q field 650. Here, the formatterdetermines that there is not enough room to place the 7-symbol WS 630and the 1-symbol postamble 610 before Q field 650 since the number ofsymbols 680 is seven, so WS 630 is instead placed immediately after Qfield 650 starting in the symbol that is reserved for the preamble.Extra symbols 620 are placed before Q field 650. As the ISG alreadyincludes preamble 640 for data sector fragment 660, the reservedpreamble symbol immediately after Q field 650 does not have to be usedas such. Likewise, extra symbols 620 use the reserved postamble before Qfield 650 since the ISG already includes postamble 610.

Depending on at least one of the lengths of the P fields, the Q fields,the write splice, the effective reader-writer gap, and the linear bitdensity of the media, the write splice may be too large to fit in therunt data sector fragment between the Q and the P fields. In this case,the ISG is sized so that there is room for a write splice field eitherbefore the Q field or after the P field when an ISG is interrupted byboth a Q field and a P field. This is shown in FIG. 7. WS 710 is tensymbols long and the runt data sector fragment between the Q and Pfields 720, 730 is 9 symbols long. As shown, the extras symbols 740 areplaced in the runt data sector fragment. Furthermore, the symbol length780 between the end of data sector fragment 770 and the beginning of Qfield 720 is ten—too small for the eleven symbols of WS 710 and thepostamble. WS 710 is then placed after the P field 730. The ISG lengthof thirty symbols (nine symbols each in extra symbols 740, 750, the1-symbol each preamble and postamble, and WS 710) guarantees that thewrite splice will always fit either before the Q field or after the Pfield.

With bit-patterned media, careful consideration must be given to theplacement of write splices on the media near Q fields and P fields.Again, the duration of the write splice represents a current transientin the writer circuit that would interfere with any read operation, suchas recovering a P field. In addition, preamplifiers can produce ahigh-frequency “degaussing” burst to the writer shortly after switchingout of write mode. These degaussing bursts and current transients in thewriter are preferred not to overlap any Q, P or servo field on the mediasince these fields should maintain their default “DC” magnetizationstate. Therefore, “invalid write splice” regions are defined by theformatter to prevent any portion of a write splice from overlapping a Qor P field. Protection of the servo fields is achieved automatically bythe track layout and the gaps before and after servo without the needfor additional functionality in the formatter.

Note that by calculating a single ISG size that works for every ISGlocation around each data track of a zone, and taking into account thefixed symbol length of the Q and P fields, postambles, preambles andother overhead, the formatter ensures that all data tracks within arecording zone have the same physical track layout and the same sectorcapacity. This is so regardless of how the runt data sector fragmentsize between Q and P fields varies with a transducing head skew angleand the linear bit density, and regardless of any particular transducinghead reader-writer gap size. This small tradeoff in format efficiencyallows for significant reductions in firmware and manufacturingcomplexity.

A method for calculating the symbol length of the ISG is shown in FIG.8. The method considers whether postamble and preamble fields are usedaround the Q fields. Also, the minimum and maximum runt data sectorfragment symbol lengths Runt_(min), Runt_(max) between the Q and Pfields for the corresponding recording zone have been pre-calculated, ashas the worst-case write splice symbol length. Here note that the symbollength of the runt data sector fragment may vary in a zone because thereader-writer gap may vary due to head skew changes over that zone. Ifthe reader-writer gap increases so as to encroach upon the symbolpreceding the Q field, that symbol will be included in the Q field. Butthe symbol at the other end of the Q field will be added to the adjacentrunt data sector fragment. The result is that the Q fields stay the samelength as well as the total number of symbols in the data sectorfragments. To further explain this result, consider FIG. 2 b where the Qfields 202 would be shifted one symbol earlier in the data wedge oftrack N. Then the adjacent runt data sector fragment length wouldincrease by one symbol. In this case track N can still be included inthe zone with the other tracks shown.

Returning to FIG. 8, the method starts at step 800, then proceeds tostep 810 to determine if postambles and preambles are used around the Qfields. If no, the method proceeds to step 820 to determine if the WSsymbol length is less than or equal to Runt_(min). If yes, the methodproceeds to step 825 where the intersector gap symbol length is setequal to the write splice symbol length times 2, then minus 1 plus thepreamble and postamble symbol lengths. If no, the method proceeds tostep 830 to determine if the WS symbol length is greater thanRunt_(max). If yes, the method proceeds to step 835 where theintersector gap symbol length is set equal to the write splice symbollength times 2, then minus 1 plus Runt_(max). If no, the method proceedsto step 840 where the intersector gap symbol length is set equal to thewrite splice symbol length times 3, then minus 2.

Returning to step 810, if postambles and preambles are used around the Qfields, the method proceeds to step 850 to determine if the WS symbollength is less than or equal to Runt_(min). If yes, the method proceedsto step 855 where the intersector gap symbol length is set equal to thewrite splice symbol length times 2, then minus 1. If no, the methodproceeds to step 860 to determine if the WS symbol length is greaterthan Runt_(max). If yes, the method proceeds to step 865 where theintersector gap symbol length is set equal to the write splice symbollength times 2, then minus 1 plus Runt_(max) minus the preamble andpostamble symbol lengths. If no, the method proceeds to step 870 wherethe intersector gap symbol length is set equal to the write splicesymbol length times 3, then minus 2 minus the preamble and postamblesymbol lengths.

From steps 825, 835, 840, 855, 865 and 870 the method proceeds to step880 to determine if the intersector gap symbol length is less than thewrite splice symbol length plus the preamble and postamble symbollengths. If yes, the method proceeds to step 890 where the intersectorgap symbol length is set equal to the write splice symbol length plusthe preamble and postamble symbol lengths. Then the method terminates atstep 899. If no, the method terminates at step 899.

Alternatively, the BPM formatter could be designed to lay out smallerISGs where they are not interrupted by a Q or P field, and larger ISGswhere interruptions require the write splice to be shifted to a latermedia position. Refer to FIG. 7 that shows a larger ISG than the ISG inFIG. 4. However, with this approach, track layouts and capacities willvary within a recording zone, from head to head, and from drive todrive. This adds to the complexity of the disc drive firmware.

Referring back to FIG. 1 b, disc formatter 60 models the BPM with symbolresolution, where a symbol can be defined as a unit of data transferredbetween formatter 60 and read channel 50 in one clock cycle. A symbolsize can be 12 bits. All fields in the data wedges between servo fieldspreferably are defined in terms of integer numbers of symbols. Thesefields include Q fields, P fields, the gaps before and after the servofields, data sector fragments, intersector gap fields, write splicefields, preamble fields and postamble fields.

The interface between formatter 60 and channel 50 uses a preferredLong-Latency Interface (LLI) protocol. An LLI protocol allows thisinterface to have a different transfer rate than the interface betweenchannel 50 and the BPM. The LLI also supports the data sector fragmentdescriptor flow (explained below) from formatter 60 to the channel 50.

The general interface between channel 50 and formatter 60 includes aclock interface that includes NRZ_CLK and WRT_CLK, and a controlinterface that includes RS, WRS, STARTING_WS, ENDING_WS, FRAG_START,FRAG_LEN, FRAG_NUM, END_OF_SCTR and BLOCK_INFO. The general interfacealso includes a data interface that includes NRZ_RDATA, NRZ_EP,RDATA_VALID, NRZ_WDATA, NRZ_PARITY, WDATA_VALID, CBF, CHAN_RDY, andFLAW_SCAN_BUS. The control interface is driven by formatter 60 andcontrols the real-time, access functions relative to the BPM. The datainterface is bidirectional and controls the movement of data betweenchannel 50 and formatter 60. Signals sent from channel 50 to formatter60 are synchronous to the NRZ_CLK from channel 50. Signals sent fromformatter 60 to channel 50 are synchronous to the WRT_CLK from formatter60.

NRZ data symbols transferred across the NRZ_RDATA and NRZ_WDATA busesare each one symbol wide. Media data symbols transferred to and from theBPM contain channel-encoded data and have the same number of bits as theNRZ_RDATA bus. Since some media data symbols include parity bits (and insome cases may include pad bits or other overhead) generated by channel50, there are more media data symbols in a sector stored on the mediathan there are NRZ data symbols in a sector transferred on the datainterface between formatter 60 and channel 50. Thus the data sector sizetransferred across the general interface (“NRZ sector size”) is not thesame size as the data sector saved on the media (“media sector size”).

NRZ_CLK from channel 50 is generated by dividing the channel 50 data PLOclock by the NRZ_RDATA bus width (NRZW). The formatter uses the NRZ_CLKto count the data wedge symbols and maintain synchronization to the discmedia. When the formatter counts a number of NRZ_CLK cycles, it knowsthat number represents the number of 12-bit media symbols that havepassed the transducing head during that same time (regardless of whatinformation is or is not stored in those media symbols). Preferably,then, the read channel does not “stretch” the NRZ_CLK or change thephase of the NRZ_CLK in any way during the data wedge to compensate forthe difference in NRZ and media sector sizes. Because of that, channel50 and formatter 60 are programmed to know both the NRZ sector size (inNRZ data symbols) and the media sector size (in media data symbols).

For each data sector fragment on the media, formatter 60 calculates thedata wedge format and transfers an information packet to the channel 50.The information packet provides data access information to the channelsuch as the amount of data to be accessed, data identification and/oroverhead information. For the following description, the informationpacket will be exemplified as a “fragment descriptor.” Each fragmentdescriptor preferably transfers six parameters in one or a predeterminedsmall number of consecutive WRT_CLK cycles, beginning at the assertionof a read signal (RS) or a write signal (WRS). The following sixparameters are included in the fragment descriptor: Sector FragmentStarting Write Splice, Sector Fragment Ending Write Splice, SectorFragment Start, Sector Fragment Length, Sector Fragment Number, and EndOf Sector flag.

Note that for the fragment descriptors, the term “sector fragment” isdifferent from the term “data sector fragment” used to this point. Asector fragment can include multiple data sector fragments. SectorFragment Starting Write Splice specifies where the write splice beginsat the start of a sector fragment. Sector Fragment Ending Write Splicespecifies where the write splice begins at the end of the sectorfragment. Sector Fragment Start specifies where the sector fragment'sstarting preamble field begins. Sector Fragment Length specifies thenumber of symbols in the sector fragment. The Sector Fragment Numberrefers to the sector fragment number within the sector fragment'scorresponding sector and is included in the interface to help ensuredata sequence synchronization between formatter 60 and channel 50. Thefirst sector fragment of any sector is defined as sector fragment 0. TheEnd Of Sector flag is asserted for the last sector fragment of everysector, giving channel 50 advance notice that the corresponding sectorfragment will complete the sector or otherwise generate a fault withinchannel 50.

The values for Sector Fragment Starting Write Splice, Sector FragmentEnding Write Splice and Sector Fragment Start refer to the correspondingsymbol position measured from the beginning of the data wedge andcounted up from zero. For this purpose, the beginning of the datawedge—“symbol zero”—is the first symbol of the first P field after theservo field. In each data wedge, data is not stored on the media priorto the first P field.

For read channels that are capable of writing (a specified polarity ofDC pattern) through the servo field for a split sector, the first sectorfragment of the data wedge might not have a starting write splice, andthe last sector fragment of the data wedge might not have an endingwrite splice. (For large sector sizes, the starting sector fragment andending sector fragment in a data wedge might be the same fragment.) If awrite splice does not exist, the corresponding parameter (SectorFragment Starting Write Splice or Sector Fragment Ending Write Splice)is set to a special value such as all ones. This special value tellschannel 50 that no write splice exists there on the media.

The Sector Fragment Length parameter specifies the exact number of datasymbols that will be accessed in the corresponding data sector fragment.This number does not include any overhead such as write splice fields,preamble or postamble fields, gaps before and after servo, and the extrasymbols within the Intersector Gap (ISG) area. Only data symbols areincluded in the Sector Fragment Length parameters, and all sectorfragments of a given sector sum to the media sector size that is aconstant value for a given track.

Prior to accessing data on the BPM, channel 50 and formatter areprogrammed with overhead information for the desired track. Thisprogrammed information may also be used in whole or in part for a zonethat the track belongs. The overhead information includes whetherpreambles and postambles are used, the symbol size of the preambles,postambles, WS, Q field, P field, runt data sector fragment, thelocation of the Q fields, and the NRZ and media sector symbol sizes.This information is programmed by the disc drive controller firmwareinto configuration registers 55, 65 shown in FIG. 1 b. Preferably onlyone media sector size and one NRZ sector size will be supported duringany read or write operation.

In read mode the channel 50 PLO remains locked to the media bit pattern,relative to the transducing read head. Also, channel 50 maintains acount of the symbols in each data wedge, starting with symbol zero (atthe beginning of the first P field in the data wedge). When channel 50is ready to begin reading a sector from the media, it asserts CHAN_RDYto formatter 60. Formatter 60 waits for the beginning of the targetsector to approach the transducing head, and then formatter 60 assertsRS to channel 50, if CHAN_RDY is asserted. Formatter 60 guarantees aminimum number of WRT_CLK cycles, for example 10 between RS assertionand the beginning of the corresponding sector or sector fragment on themedia, with respect to the transducing head. This minimum number ofcycles provides channel 50 enough time to decode the fragment descriptorsent at the rising edge of RS and prepare to recover the sector fragmentbefore its preamble field reaches the transducing head.

In response to the assertion of RS, channel 50 latches the fragmentdescriptor and waits for the FRAG_START-identified symbol to reach thetransducing head. Channel 50 then begins recovering the preamble symbols(if configured for preamble fields), followed by the data symbols. Atthe end of the last data symbol, channel 50 recovers the postamblesymbols (if configured for postamble fields). Note that if channel 50 isconfigured for preamble and postamble fields, a preamble field occursimmediately before the first data symbol of the sector fragment, and apostamble field occurs immediately after the last data symbol of thesector fragment, without interruptions from Q or P fields. Formatter 60,which is responsible for the media layout, controls this relationship.

During the reading of the sector fragment, channel 50 may encounter a Qfield or P field, based on its internal symbol counter and itsprogrammed Q and P field parameters. When such encounters occur, channel50 automatically pauses its data symbol decoding before the Q field or Pfield, and automatically resumes its data symbol decoding after the Qfield or P field. If preamble and postamble fields are enabled inchannel 50 configuration registers, channel 50 also automatically pausesits data symbol decoding over preamble and postamble fields.

Channel 50 internally latches the FRAG_LEN parameter at the rising edgeof the WRT_CLK cycle corresponding to the assertion of RS, so it knowshow many media data symbols exist in the corresponding sector fragment.If a sector fragment ends prior to the end of the sector due to a servofield split, the split likely breaks a single sector fragment into twofragments. In this case, channel 50 pauses its decoding process whilethe transducing head is over the servo sector and continues decodingwhen more user data is read after the servo sector.

When channel 50 is ready to send decoded data to formatter 60, itasserts RDATA_VALID to formatter 60. Every NRZ_CLK cycle for whichRDATA_VALID is asserted transfers one NRZ_RDATA symbol of decoded userdata to formatter 60. In an optional wedge operation mode, channel 50transfers all the data to formatter 60 contiguously for every wedgedata, so the RDATA_VALID does not deassert except at the wedgeboundaries. Channel 50 does not send preamble or postamble data over theNRZ_RDATA bus. As channel 50 decodes the user data from the recoveredsector, it sends the decoded user data to the formatter over theNRZ_RDATA interface independently of the control interface's timing andcan be delayed by a number of NRZ_CLK cycles relative to the sectorlocation on the media.

During write operations, formatter 60 begins transferring data tochannel 50 before WRS is asserted so that channel 50 has enough dataqueued to encode the first NRZ_WDATA symbols prior to the assertion ofWRS. Subsequent encoded media data symbols are available in channel 50at the NRZ_CLK transfer rate. Formatter 60 transfers data to channel 50across the NRZ_WDATA bus by asserting WDATA_VALID during each WRT_CLK,as long as channel 50 does not assert the CBF (Channel Buffer Full)signal. Formatter 60 keeps channel 50's write data FIFO full enough tosatisfy channel 50's data encoder at all times during the write process.When the channel 50 encoding pipeline is temporarily full, it assertsCBF to force formatter 60 to pause the data transfer. Formatter 60 doesnot send more data to channel 50 until CBF has been deasserted. Ifchannel 50 detects an internal write data pipeline under-run during thewrite process, it alerts the formatter by asserting CHAN_FAULT. Channel50 counts the media data symbols as it removes them from its encodingpipeline, to determine the location of the media sector boundary.

Formatter 60 waits for the target sector to approach the transducinghead, and then asserts WRS to channel 50 a minimum number of WRT_CLKcycles prior to the location of the write splice reaching the writehead. On the same WRT_CLK cycle for which formatter 60 asserts WRS,formatter 60 provides a fragment descriptor.

When channel 50 has encoded enough data such that it is ready to beginwriting a sector to the media, it asserts CHAN_RDY to formatter 60.Formatter 60 is not allowed to begin a write-to-media operation (byasserting WRS) until CHAN_RDY has been asserted. The formatter 60 checksthe state of CHAN_RDY before asserting WRS at the beginning of eachsector. For split sectors, CHAN_RDY is not checked before writing sectorfragments after the first sector fragment.

Further during a write operation, the formatter 60 control interfacesends a fragment descriptor to channel 50 at the rising edge of WRS.STARTING_WS indicates the symbol count into the data wedge at whichchannel 50 is to assert write preamplifier out (WRPO) to start the writesplice at the beginning of the sector fragment, unless WRPO is alreadyasserted from writing the previous sector. If WRPO is already asserted,it will remain asserted for this sector fragment. ENDING_WS indicatesthe symbol count into the data wedge at which channel 50 is to deassertWRPO to start the ending write splice for the sector fragment, if thenext sector is not being written. If the next sector is also beingwritten, WRPO will remain asserted. FRAG_START indicates the symbolcount into the data wedge at which the preamble field starts for thesector fragment. FRAG_LEN indicates the number of encoded data symbolsin the sector fragment, excluding any preamble and postamble fields, andalso excluding any Q or P field interruptions of the data on the media.FRAG_NUM indicates the fragment number, relative to the beginning of thesector (where non-split sectors will always have a fragment number ofzero). END_OF_SCTR indicates whether the sector fragment ends thecorresponding sector on the media. (END_OF_SCTR will always be true fornon-split sectors.)

Since channel 50 begins encoding the user data in advance of thecorresponding write event to the disc media, the channel 50 encoder doesnot know where any servo splits might occur. Therefore, channel 50encodes data without regard to servo splits in the sectors. Similarly,the channel 50 sector encoding operation is independent of the locationsof any temporary interruptions of the sector data that may occur due toQ or P fields on the media.

Again, the fragment descriptor is transferred to the channel 50 when WRSor RS is asserted, which occurs a predetermined minimum number ofWRT_CLK cycles prior to the beginning of the sector fragment relative toeither the read head or the write head. This number is determined bychannel 50 processing delays and can be less than 10 WRT_CLK cycles forexample. Thus, RS and WRS do not directly trigger the corresponding reador write activity in channel 50. In other words, RS and WRS do notindicate when data is ready to be accessed at the transducing head.

In more detail, due to the precision of the media write process for BPM,accessing sector fragments on the media via real-time Write Gate or ReadGate signaling from the formatter to the read channel is inadequate.Therefore, RS and WRS assertions will precede the corresponding sectorfragment starting locations relative to the transducing head by apredetermined number of WRT CLK cycles, since the starting positions ofthe fragments on the media are determined by the data access informationtransferred across the FRAG INFO bus, not strictly by the location ofthe rising edge of RS or WRS.

Also, WRT_CLK is preferably generated from channel 50 NRZ_CLK. Thisallows the interface between channel 60 and formatter 50 to beisochronous.

To initially assert RS or WRS at the beginning of a data wedge,formatter 60 receives a signal generated relative to a servo addressmark by the disc drive servo-related functionality on lead 65. Theassertion of this “early servo gate” signal occurs around thedeassertion of the servo gate signal minus the predetermined minimumnumber of WRT_CLK cycles described above. The early servo gate signal isas a reference point for formatter 60 to assert either RS or WRS beforethe beginning of each data wedge. And a symbol counter in the formatterstarts to count the data wedge symbols in response to the early servogate signal. The output of the counter is used to time any additional RSor WRS from the formatter for that data wedge. That timing takes intoaccount the channel encoding and decoding time. Preferably RS and WRSare asserted 10 WRT_CLK cycles prior to the data on the media beingaccessible by the transducing head.

FIG. 13 illustrates one method for the use of RS and WRS. After startstep 1300, data access information is latched responsive to RS or WRS atstep 1310. At step 1320 a data access is initiated using the data accessinformation. However, the data access is initiated independent of thetiming of RS or WRS.

For system-on-chip implementations, bus 70 is intended to be wide enoughto transfer each fragment descriptor in one WRT_CLK cycle. However,other configurations with fewer signals and requiring multiple WRT_CLKcycles to transfer each fragment descriptor are also feasible, if theyare supported both by formatter 60 and channel 50.

The timing diagram in FIG. 11 illustrates an example of a data wedgeformat with the corresponding WRS signal generated by the formatter. Thetrack portion designated “media” represents the timing of the actualdata under the transducing head. The track portion designated “FmtrView” represents a spatial time shift of the “media” track portion thatthe formatter is generating. This formatter view of the data wedgeprecedes the actual media position at the write head, allowing the earlytransfer of the fragment descriptors to the channel. This is shown astiming interval 1110. The beginning of that interval relates to theearly servo gate signal described above.

The “Sector Layout” represents how the formatter takes into account thedata sectors and associated overhead layout in the data wedge. The WS(write splice) signal indicates where the formatter has determined eachwrite splice is located in the format. The Invalid_WS signal indicatesevery symbol position in the data wedge at which a write splice is notallowed to begin, for protection of the Q and P fields. And as shown,the write splice length is short enough that it can fit in the runt datasector fragments between the Q and P fields, as shown in the intersectorgap between sectors 1 and 2. The “Q” and “P” signals represent theplacement of the Q and P fields as programmed in the formatter.

The signal SWCE (Sector Word Counter Enable) indicates when theformatter's data symbol counter counts encoded data symbols for acorresponding sector fragment. The wedge symbol counter, as representedby the Count Enable signal, counts up for the entire data wedge. Thisgives the formatter a precise representation of the length of the entiredata wedge.

The three rising edges of WRS transfer the three fragment descriptors tochannel 50. The WRS signal from the formatter is shown as approximatelyenveloping an entire sector fragment, including any Q or P fields thatare contained within the fragment. This is optional, however, since allthe information about a sector fragment is transferred to channel 50 onthe rising edge of WRS. Though by making the WRS pulse widthsapproximate the sector fragment size on the media, the formatter canprovide this signal to an externally accessible port as a usefuldiagnostic function. Also WRS is deasserted a small number of symbolsbefore the end of the sector fragment to allow the formatter to preparethe next fragment descriptor (if not already done) and assert WRS forthe next sector if the next sector is to be transferred.

Channel 50 maintains a symbol counter from the beginning of the datawedge starting immediately after the servo field. An additional benefitof using a symbol counter rather than a bit counter is that it willreduce the amount of additional high-speed digital logic in channel 50.The symbol counter can also be used to synchronize timing between theformatter and the channel. In write mode, while actively writing to themedia, channel 50 automatically holds the write data to a predetermined(possibly programmable) DC level when the writer is over the Q fields orthe P fields.

Specifically, channel 50 does not transition the write current (eitherby changing the write data or by turning the preamplifier on or off)while the reader is over a P field. Channel 50 does not cause thepreamplifier to exit write mode if the writer is over a P or if thewriter will be over a P field before the write splice time expires. Thisalso supports preamplifiers that generate a high-frequency “degaussing”burst to the writer during the write current turn-off period.

The location and size of the Q fields in channel 50 are programmable.Instead of phase locked loop and sync fields, each sector will beginwith a write splice field. Channel 50 is programmed with the size ofthis write splice field, which will potentially vary with recordingzone, but will not vary on a given data track. Optionally, split sectorsalso include a write splice field before and after the servo field, ifwriting through servo fields cannot be supported (for example, due tothe use of repeatable run-out fields or other data fields written intoeach servo field).

Channel 50 automatically writes a default (possibly 2T) pattern duringthe write splice field when writing to the media, and will automaticallyskip the write splice field when reading from the media. As describedabove, the BPM architecture will support preamble fields at thebeginning of each contiguous run of sector data and postamble fields atthe end of each contiguous run of sector data, to provide opening andclosing sequences for the maximum-likelihood decoder in the channel.Channel 50 is programmed with the preamble field size and the postamblefield size, which will not vary on a given data track.

For determining the fragment descriptors, formatter 60 calculates thedata format for the upcoming data wedge. To do that, either theformatter has already calculated an immediately previous data wedgeformat and can use that to calculate the upcoming data wedge format. Orthe formatter has to catch up to understand the previous data wedgeformat, particularly if a data sector was split across a servo wedge.This catch up can occur when the transducing head has moved tracks.

First, the formatter understands what servo wedge, actual or logical, itis over. Next the formatter determines if the first data sector fragmentof the upcoming data wedge is part of a split data sector or begins anew data sector. This determination is done by the formatter usinganother model of the data wedge as a contiguous group of data sectorfragments (with the Q and P fields removed, along with their reservedpostamble and preamble fields) as shown in FIG. 9. A data format of datawedge 900 is shown between two servo wedges. Data wedge 900 includesdata sector fragments D, Q and P fields, and preamble and postamblefields. However, for purposes of this determination, the formatterdiscards the Q and P fields along with the associated preamble andpostamble fields (the transducing head overhead), and ignores the gapsbefore and after the servo wedges. In this way, the formatter onlyconsiders the data sector fragments shown as 900′. The data sectorfragments in 900′ are effectively concatenated data. Note that for thisconcatenated data model the data sector fragments include all writesplices, ISGs, and the non-reserved preambles and postambles. The writesplices, ISGs, and non-reserved preambles and postambles can beconsidered individually and collectively as fragment overhead.Non-overhead includes the actual data that can be considered as datasymbols.

In addition, the formatter takes into account that the overhead—Q and Pfields, ISGs, preambles, postambles, write splices, gaps before andafter servo—within each data wedge of a track are constant, regardlessof how data sectors are interrupted by Q and P fields. Every ISG fieldon the track is the same size. Every write splice field is the samesize. Every Q field is assumed to have a postamble field immediatelybefore it and a preamble field immediately after it. (Preamble andpostamble fields may not be required around the Q fields; in this case,these preamble and postamble fields will be assumed to be zero-length.)Every P field is assumed to have a preamble field immediately after it,and every P field except the first one in each data wedge is assumed tohave a postamble field immediately before it. If a gap after servo (GAS)field is required (for example, to contain repeatable timing run-outinformation), it occurs after the first P field of every data wedge.Given all that, the data sector fragments 900′ have the same number ofsymbols for each data wedge of a track. That can extend to all or partof the tracks that make up a recording zone.

Using the fact that the data sector fragments 900′ have the same numberof symbols for each data wedge of a track, the formatter can quicklydetermine the upcoming data wedge's data format. For example, considerthat a transducing head settled on a new track. The first servo wedge itencounters is servo wedge 2. With the formatter knowing that each datasector size is X and the data sector fragments 900′ total size is Y, theformatter divides Y by X and then multiplies the result by the number ofpreceding data wedges (2 in this case). Any remainder starts the datasector fragment immediately after servo wedge 2. The formatter can thenstart generating the fragment descriptors knowing the lengths andlocations of the overhead symbols and the symbol lengths of the datasector and data sector fragments 900′. All fragment descriptors for adata wedge can be determined at the same time and then queued.

If writing through the servo fields is supported by the disc drive, theformatter defines the capacity of a data wedge that begins with a newsector (e.g., “wedge 0” on the data track), since these types of datawedges will be slightly smaller in capacity compared to data wedges thatbegin with a split sector. This slightly reduced capacity of “wedge 0”type wedges is due to the fact that wedges that start with a new sectorwill begin with a write splice, whereas wedges that begin with a splitsector will not begin with a write splice.

The data wedge model works well for the formatter to determine if theupcoming data wedge starts with a split data sector, but it can create atiming issue if the fragment descriptors are generated using only thesame model without accounting for the locations and sizes of the Q and Pfields. If the formatter did not consider the placement of the Q and Pfields, the formatter would assert RS or WRS earlier and earlier for thenext sector as it traversed the data wedge. Asserting WRS earlier thannecessary for a target sector would increase the likelihood that channel50 would not have encoded write data ready for the next sector justbefore WRS is asserted. This timing issue could put additional stress onthe channel's data encoding pipeline, and it is considered undesirable.

This formatter model allows the quick calculation of the splitconfiguration at the end of any data wedge, given the splitconfiguration at the beginning of the data wedge. It also allows for thequick calculation of the impending data wedge format based on the actualor logical servo wedge zero. This model also allows for substantial useof different formatter configurations.

The determination of the fragment descriptors will be explained withreference to FIGS. 10 a and 10 b. FIG. 10 shows a data wedge 1000between servo fields 1010. Data wedge includes 4-symbol P fields 1020,7-symbol WS 1030, 1-symbol preambles 1040, 1-symbol postambles 1050,5-symbol Q fields 1060, 4-symbol runt data sector fragments 1070 and1072, 6-symbol extra symbols 1080, 2-symbol extra symbols 1082, 4-symbolextra symbols 1084, 1-symbol gap before servo 1090. Also included aredata sector fragments 1001-05 that are respectively 32-, 16-, 16-, 42-and 20-symbols in length. The data format of data wedge 1000 isexemplary only, and as such is not limiting. So are the symbol lengthsand positions of the fields. The symbol lengths for the WS, the runtdata sector fragments, the Q and P fields, the preambles and postambles,and the gap before servo were predetermined and are available to theformatter. The extra symbols length can be calculated using the methodsteps shown in FIG. 8.

The table in FIG. 10 b shows the fragment descriptors for data wedge1000. Again note that for the fragment descriptors, the term “sectorfragment” is different from the term “data sector fragment” used to thispoint. A “sector fragment” can include multiple “data sector fragments”as will be seen referring to this table. The first entry in the table isfor fragment descriptor N. The Sector Fragment Start Write Splice forthis sector fragment is at symbol 4 (the first symbol in the P field1020 is symbol 0). The Sector Fragment End Write Splice is at symbol 78.Thus, “data sector fragments” 1001, 1002 and runt data sector fragment1070 are included in “sector fragment” N. The Sector Fragment Start isthe symbol location for the preamble of data sector fragment 1001, whichis preamble 1040 at symbol 11. The Sector Fragment length is the sum ofdata sector fragments 1001, 102 and runt data sector fragment 1070,which is 52 symbols. The Sector Fragment Number is shown as 2, meaningthere are Sector Fragment Numbers 0 and 1 in a previous wedge. End ofSector Flag is set to 1 to signify that Sector Fragment Number 2 is thelast sector fragment in the associated data sector. Similardeterminations are made for Fragment Descriptors N+1 and N+2.

The defined architecture allows for format-efficient data storage onbit-patterned media, while allowing for typical variations in the drive,such as reader-writer gap variations. The defined BPM architecturerelaxes some timing requirements on real-time signaling from theformatter to the channel, while enabling bit-accurate alignment betweendata accesses and the media.

The description above is applicable for systems in which the channel andthe formatter are integrated as parts of the same “system on chip”, orSoC. Therefore, separate read and write data buses have been usedinstead of a bidirectional bus with bidirectional control signals.However, there may be circumstances where a discrete, external formattermay be used to interface to an external channel. The read and write databuses can then be combined into a single bidirectional bus to reduceoverall pin count.

The detailed description is illustrative only and is intended not tolimit this disclosure. Variations and modifications are possible. Forexample, the functionality can be performed by hardware alone, orhardware under firmware control. Either or both of the FRAG_NUM and theEND_OF_SCTR can be removed from the fragment descriptor. Any of thefields do not have to be symbol aligned. The units on the interfacewould then be defined as something other than symbols. Bits instead ofsymbols can be used. Although the length of the Q field is determined bythe length of the P field as described to be as short as possible tosatisfy the timing recovery requirements, the Q field can be the samesize as the P field depending on the resolution the interface uses. TheQ field can also be greater than or equal to the length of the P field,constrained by any physical limitations of format efficiencies takeninto account.

The runt data region space can be eliminated so that the entirereader-writer gap can be just Q and P fields. The Q field could run intothe P field, leaving no usable media between them. However, thissituation would represent a significant format efficiency loss, which isless desirable. The write splice can be any size. The interface protocolsupports a wide range of write splice lengths. Smaller is better forformat efficiency. The preambles and postambles can be any size. Theinterface protocol can support preambles and postambles longer than onesymbol. The formatter implementation is simplified by assuming they canbe no longer than one symbol. The preamble and/or postamble can beeliminated from the ISG. However, induced bit errors may occur. The ISGdoes not have to include extra symbols. Including extra symbols in theISG helps to keep the formatter logic less complex. A symbol can beanything less than a sector in size. The symbol width is chosen to be apractical unit of data transfer and timing management for both the readchannel and the formatter.

The interface described could be used with other types of media, such asnon-bit-patterned media, heat assisted magnetic recording media, tapeand optical. The interface described can be used for a digital datastream coupled to the channel. To illustrate, FIG. 12 shows a formatter1200 and channel 1205 coupled to one of a tape 1210, optical 1215 anddata stream 1220.

The described apparatus and methods should not be limited to theparticular examples described above. Various modifications, equivalentprocesses, as well as numerous structures to which the describedapparatus and methods may be applicable will be readily apparent.

What is claimed is:
 1. A formatter comprising: a first output to providedata access information; and a second output to indicate the data accessinformation is ready for transfer, the second output is timedindependent of initiating a data access.
 2. The formatter of claim 1wherein the data access information includes at least one fragmentdescriptor.
 3. The formatter of claim 1 wherein the second output isprovided a predetermined time before associated data is available. 4.The formatter of claim 3 wherein the second output is generatedresponsive to an early servo gate signal.
 5. The formatter of claim 1further comprising a third output to provide formatted data.
 6. Theformatter of claim 5 further comprising a fourth output to provide aclock signal.
 7. The formatter of claim 1 further comprising a firstinput coupled to receive formatted data.
 8. The formatter of claim 7further comprising a second input coupled to receive a clock signal. 9.The formatter of claim 1 configured to use a concatenated data model togenerate a data wedge format, and to use the data wedge format togenerate the data access information.
 10. The formatter of claim 1wherein the data access information includes at least one of a sectorfragment starting write splice value, a sector fragment ending writesplice value, a sector fragment start value, a sector fragment lengthvalue, a sector fragment number and an end of sector flag.
 11. A devicecomprising: a formatter that outputs an information packet and a signalthat indicates the information packet is ready; and a channel coupled toreceive the information packet and the signal, the channel initiates adata access independent of the signal.
 12. The device of claim 11wherein the formatter and channel operate isochronously.
 13. The deviceof claim 11 wherein the formatter receives an early servo gate signal.14. The device of claim 11 wherein the gate signal is not used toinitiate a data access.
 15. The device of claim 11 wherein the channelprovides a first clock signal to the formatter.
 16. The device of claim15 wherein the formatter provides a second clock signal to the channelthat is responsive to the first clock signal.
 17. The device of claim 11further comprising a bit-patterned medium in communication with thechannel, the bit-patterned medium configured to have at least one zoneincluding a plurality of tracks, at least some of the plurality oftracks have transducing head overhead and concatenated data that are thesame size, respectively.
 18. The device of claim 17 wherein theformatter generates a data wedge layout using the same size transducinghead overhead and concatenated data, and generates the informationpacket using the data wedge layout.
 19. The device of claim 11 furthercomprising a medium that includes data wedges, each data wedge has sameamounts of data symbols and overhead.
 20. The device of claim 11 whereinthe information packet includes at least one of a sector fragmentstarting write splice value, a sector fragment ending write splicevalue, a sector fragment start value, a sector fragment length value, asector fragment number and an end of sector flag.
 21. A data formattingmethod comprising: outputting at least one fragment descriptor for adata access; and outputting a signal that indicates the at least onefragment descriptor is available and that is timed independent of astart of the data access.
 22. The method of claim 21 wherein the atleast one fragment descriptor sector includes fragment information. 23.The method of claim 21 wherein the at least one fragment descriptorincludes at least one of a position, length and number information. 24.The method of claim 21 wherein the at least one fragment descriptorincludes at least one of a sector fragment starting write splice value,a sector fragment ending write splice value, a sector fragment startvalue, a sector fragment length value, a sector fragment number and anend of sector flag.
 25. The method of claim 21 wherein the signal isgenerated responsive to an early servo gate signal.